The ureter is a fibromuscular tube that conveys urine from the kidney to the bladder. The ureter begins with the renal pelvis and enters the bladder at an area called the trigone. The bladder trigone is the triangulated area between both ureteral orifices and the bladder neck. A normal length for an adult ureter is approximately 16 to 18 inches.
Ureteral stenosis, stones in the ureter, and other medical conditions call for the use of a ureteral stent or prosthesis. Currently available types of indwelling ureteral stents are variations of the same basic tube structure. The outer and inner diameter, and the size of the drainage holes or the retention elements that are to be placed in the kidney and bladder vary among the known stent types. None of the known ureteral stents adequately address the pain generally associated with an indwelling ureteral stent.
Ureteral pain associated with a stent is thought to arise from the following: 1) contact between the stent and the mucosal lining of the ureter, or, especially, with the bladder trigone; 2) flank pain from vesico-ureteral reflux which occurs primarily during voiding; and 3) irritation caused by the stent in the intramural tunnel of the urinary bladder wall which is 1-2 cm proximal to the ureteral orifice.
After an invasive surgical procedure to remove a kidney stone from a patient's ureter, the lining of the ureteral lumen tends to be swollen and inflamed. Post-surgical stent placement, therefore, poses a particular challenge in terms of patient comfort.
Pain and discomfort associated with indwelling stents or prostheses is not unique to the ureter. Other body canals, for example, blood vessels such as the coronary vessels, and bile ducts, can also benefit from a new stent design that alleviates the pain associated with stents while maintaining the patency of the body canal.
In addition, an interventional device such as a stent that can better accommodate the anatomy of body canals is needed. Such a device would not only conform to the shape and length of a body canal, the device would also adjust, preferably automatically, to changes in the shape and length of the body canal that occur, for example, during normal bodily functions.